"I've heard the term 'scraping' used in regards to how some mobile site platforms build a mobile site. What is it? Is it good or bad?"
Scraping involves, in a nutshell, copying images and text from a desktop site and then embedding that content into pre-designed mobile site templates. As with most things, there are upsides and downsides.
Scraping IS easier and it IS faster. But! As desktop content was developed with desktop monitor real estate in mind, the results can end up not providing the desired user experience. Graphics and text may not be formatted correctly and RSS feeds may display improperly, for example. Users also have little to no ability to revise or edit the template if they dislike the results and want to better tailor how content is displayed on the site.
Another thing to keep in mind - scraping requires the existence of a desktop site. If you don't have a desktop site, the mobile web platform that relies solely on scraping will not be able to function.